The stria vascularis of the mammalian cochlea produces the endocochlear potential (EP) and may also produce the intracellular-like Na ion/K ion ratio in scala media. Probably both the EP and endocochlear Na ion /K ion are necessary for normal functioning of the inner ear. Carbonic anhydrase and Na ion-K ion adenosine triphosphatase have been found in vitro in the stria. In the proposed study, proteins of the stria will be fractionated by microtechniques and their properties relevant to ion transport will be determined. The EP and Na ion/K ion ratios of the intact cochlea will also be determined in order to correlate physiological and biochemical results.